1. Field of the Invention
The present invention relates to a dual band phased array antenna apparatus for a radar or the like.
2. Description of the Related Art
Phased array antenna elements have been used for generating a scanning beam. In this case, each of the antennas are powered by different phased power signals. Generally, since the scanning beam is a high frequency pencil-type beam, a large search time for the entire elevation and azimuth angle coverage is required, while high acquisition and tracking performance for three-dimensional information regarding a near object is maintained. This will be explained later in detail.
Note that, in order to reduce the search time for the entire elevation and azimuth angle coverage in a long distance (range) area, a low frequency antenna can be used. That is, a maximum radar distance (range) of the low frequency antenna can be larger than that of the high frequency antenna for the following reasons. First, the output power of a power amplifier in a transmitter of a transceiver module can be high. Secondly, the noise figure of a low noise amplifier in a receiver of the transceiver module can be low. Thirdly, the loss of feed lines can be small. Fourthly, the propagation loss in the air is small. As a result, the low frequency scanning beam can propagate a long distance and be received from a distant object to form two-dimensional information. However, the resolution and angle accuracy of a radar system using the low frequency scanning beam is poor, and as a result, the acquisition and tracking performance for a near object is reduced.
In order to make use of both the high acquisition and tracking performance of the high frequency scanning beam for a near object and the small search time for the entire elevation and azimuth angle coverage by the low frequency scanning beam for a distant object, dual band array antenna elements have been known (see: J. R. James et al.: "Superimposed dichroic microstrip antenna arrays", IEE. PROCEEDINGS, Vol. 135, Pt. H, No. 5, Oct. 1988). That is, a plurality of first array antenna elements for the low frequency radiation beam and a plurality of second array antenna elements for the high frequency radiation beam are superimposed on each other. This will be explained later in detail. Note that the above-mentioned document does not disclose an arrangement of transceiver modules to the array antenna elements. One approach to this is that each of the array antenna elements may be connected to one transceiver module. In this case, however, the antenna apparatus is increased in size and cost, since the antenna apparatus is too complex. At worst, it is impossible to arrange all of the necessary transceiver modules due to the mounting space therefor. Also, even when a low frequency scanning beam is used, a searching time for the entire elevation and azimuth angle coverage regarding a distant object is still large, since the low frequency radiation beam is a pencil-type.